(A) Alpha-lactalbumin (alpha-LA)-like proteins modify the activity of N-acetyl-glucosaminide beta 1-4 galactosyltransferase and their expression is regulated by hormones. We have isolated and sequenced entire mammary gland alpha-LA gene, including its 5'-flanking sequences. The gene sequences were compared with chicken lysozome gene, since it was proposed that the two genes have arisen from a common ancestral gene. These studies show: 1) alpha-LA and lysozome genes contain 3 introns at similar positions. The first three exons show high nucleotide homologies; 2) 5'-flanking sequence of alpha-LA gene has several identical short repeat sequences. Some of these sequences resemble the concensus sequences which bind hydrocortisone and progesterone receptors which modulate the expression of this gene; and 3) the fourth exon of alpha-LA, which partly codes for the C-terminal residues of the protein, essential for its interaction with galactosyltransferase, is markedly different from the corresponding exon of lysozome gene and is preceded by two (TG) repeats-(TG)21 and (TG)24. It is suggested that the 4th exon of alpha-LA coding for a new functional unit might have replaced the DNA region of primordial lysozome gene and led to a protein with a new function. (B) Rat whey phosphoprotein (Wp) has a double domain structure with striking homologies to a protease inhibitor. Wp-gene expression is regulated by the same set of hormones as the alpha-LA gene. Rat Wp-gene has been isolated and its full sequence is nearing completion. The gene structure and nucleotide sequences show that: a) there are three intervening sequences in the entire gene which is 2.5 kb in length; b) second and third exons code for first and second domains of the protein, respectively; and c) first and the third intervening sequences encompassing the second and third exons, have several repeat and inverted repeat sequences.